Manufacturing method for a gas sensing element

Abstract

A non-sintered element body having a predetermined shape is fabricated from powdery raw material of a solid electrolytic body. The non-sintered element body is temporarily sintered to obtain a partially-sintered element body as a semi-finished product of the solid electrolytic body. An outer surface of the partially-sintered element body is dipped into a slurry. The slurry contains surface roughing powder including large and small grains which are mutually differentiated in grain size. Then, the partially-sintered element body with a rough slurry film coated thereon is completely sintered into the solid electrolytic body.

What is claimed is:  
     
       1. A method for manufacturing a gas sensing element which has a cup-shaped solid electrolytic body having a reference gas chamber formed therein, an inside electrode provided on an inner surface of said solid electrolytic body, and an outside electrode provided on an outer surface of the solid electrolytic body, said manufacturing method comprising: 
       a step of forming a non-sintered element body having a predetermined shape from powdery raw material of said solid electrolytic body;  
       a step of temporarily sintering said non-sintered element body to obtain a partially-sintered element body as a semi-finished product of said solid electrolytic body;  
       a step of dipping an outer surface of said partially-sintered element body into a slurry, said slurry containing surface roughing powder including large and small grains which are mutually differentiated in grain size; and  
       a step of completely sintering said partially-sintered element body with a rough slurry film coated thereon into said solid electrolytic body.  
     
     
       2. The manufacturing method for a gas sensing element in accordance with  claim 1 , wherein a coating density of said slurry during said step of dipping the outer surface of said partially-sintered element body is in a range of 0.05 mg/mm 2  to 0.30 mg/mm 2  in terms of the amount of said surface roughing powder contained in said slurry. 
     
     
       3. The manufacturing method for a gas sensing element in accordance with  claim 1 , wherein the grain size of said large grains is in a range from 5 μm to 50 μm. 
     
     
       4. The manufacturing method for a gas sensing element in accordance with  claim 1 , wherein the grain size of said small grains is not larger than 1 μm. 
     
     
       5. The manufacturing method for a gas sensing element in accordance with  claim 4 , wherein the grain size of said small grains is in a range from 0.1 μm to 1 μm. 
     
     
       6. The manufacturing method for a gas sensing element in accordance with  claim 1 , wherein the entire content of said large grains is in a range from 5 weight % to 20 weight % when said slurry is 100 weight %. 
     
     
       7. The manufacturing method for a gas sensing element in accordance with  claim 1 , wherein the entire content of said small grains is in a range from 10 weight % to 20 weight % when said slurry is 100 weight %. 
     
     
       8. The manufacturing method for a gas sensing element in accordance with  claim 1 , wherein the step of dipping the outer surface of said partially-sintered element body into said slurry containing the surface roughing powder is performed in such a manner that a slurry film is formed on the outer surface of said partially-sintered element body, said large grains protrude from a surface level of said slurry film and are spaced from each other, and the following relationship is satisfied, 
       
         
           0.25d≦t≦0.75d  
         
       
       wherein ‘d’ represents a grain diameter of said large grains and ‘t’ represents a thickness of said slurry film. 
     
     
       9. The manufacturing method for a gas sensing element in accordance with  claim 1 , further comprising the following steps for dipping the outer surface of said partially-sintered element body into said slurry containing the surface roughing powder: 
       a step of preparing a slurry tank equipped with a stirrer therein;  
       a step of rotating said stirrer to cause rotational flow of said slurry in said slurry tank;  
       a step of dipping said partially-sintered element body in said slurry in a condition where said stirrer is rotating or stopped; and  
       a step of lifting said partially-sintered element body out of said slurry tank.  
     
     
       10. The manufacturing method for a gas sensing element in accordance with  claim 1 , further comprising the following steps for dipping the outer surface of said partially-sintered element body into said slurry containing the surface roughing powder: 
       a step of preparing a slurry tank filled with said slurry;  
       a step of rotating said partially-sintered element body about its center axis and dipping said partially-sintered element body into said slurry when a stirrer is rotated in said slurry tank, or dipping said partially-sintered element body into said slurry without rotating said partially-sintered element body when said stirrer is not rotated in said slurry tank; and  
       a step of lifting said partially-sintered element body out of said slurry tank.